My talk will consider some of the ways that it is possible to make a shell structure bistable, i.e. where the structure can be left unloaded in two different configurations.  In particular I will consider structures have the same initial geometry as a simple tape-measure; they are straight in a longitudinal direction, but have a curved cross-section.  However, unlike a tape-measure, the structures have a stable coiled configuration.  Structures using this technology are already being used as coilable masts, and have been suggested for use as components of aircraft landing gear.

Two different methods of making these shells bistable will be described.  The first depends on altering the relative bending stiffnesses of the shell using, for instance, fibre-reinforced composites.  The second requires an initial state of self-stress to be set up in the shell.  Physical examples of both types of structure will be available to show the wide range of behaviour that is possible.

A simple inextensional analytical model that captures the key properties of the shells will be descibed.  An interesting prediction of the model is that it is possible to make tubes that are neutrally stable; they have no stiffness, even for large deformations.  An example will be shown.